For accessibility purposes I need to be able to add alt tags to images for screen readers. I couldn't find anything in the user guide on alt tags. Right clicking I can see the image description, but don't see a means to edit the image description.

Is it possible to add alt tags to images? If so, how? If not is there a way to alter the image description?

I think the information you’re seeing there comes from the Finder, so you’d need to alter the filename, image dimensions, etc, in the Finder before inserting the image into your Nisus Writer document. But these are not really ALT tags in the usually accepted sense.

My experience with ALT tags has only been with (X)HTML documents. These are essentially plain text documents and hence easily created in Nisus Writer. When viewed as a text document in a word processor, though, you see the source code, complete with content and other tagged material (which will include the ALT tags). When you alter the file extension to (say) .htm, the file will open in your default Web browser and look much nicer (depending on your styles, of course — whether included in the source code or residing in a separate style sheet referenced by the main document).

So what you need to do all depends on what sort of file the user’s viewing software expects to display.

I used to use Nisus Writer Pro for this purpose, together with (if I recall correctly) a macro that toggled between .txt and .htm filetypes as required. However, these days I find the workflow quicker and simpler with BBEdit when it comes to creating and editing code. Of course, I still use NWP to create the content in the first place!

My use case is a bit different. I need to produce documents, convert them to PDFs and then post them in a learning management system. Due to ADA requirements the PDFs themselves must include readability features like alt text / tags for images.

MS Word has the capability to add these to images and even to tables that are included in the doc. I don't want to use MSW so I'm trying to figure out if I can do some of these items in NWP. I'll explore the Finder info again. I did not see an option there in 10.13 to add alt text/tags to images. If that would work, I'd be in fine shape there. I'm also exploring whether tags can be added in an image processing program like Affinity Designer. For images that don't require any real manipulation, I'd prefer not to add another step to the process of putting a simple teaching doc.